Accelerating Effect of Polyvalent Cation-Substituted Phosphates on Nucleation of Sodium Acetate Trihydrate from Its Melt

作者：Watanabe Yasuyuki^*

来源：Kagaku Kogaku Ronbunshu, 2017, 43(3): 160-166.

DOI：10.1252/kakoronbunshu.43.160

• Crystallization
• Salt Hydrate
• Nucleating Agent
• Deactivation
• Latent Heat Storage

The functional mechanism of nucleating agents added to the latent heat storage material sodium acetate trihydrate (melting point 331 K) was examined. Such nucleating agents are activated by solidification of the trihydrate melt and accelerate nucleation in the melt, but superheating of an activated agent beyond a critical temperature, upper limiting temperature, during heat storage results in its deactivation. In this study, continued from the previous study (Watanabe, 2017), 14 types of cations (Mg2+, Ca2+, (CaH)(3+), Sr2+, (BaH)(3+), Al3+, Pb2+, Cr3+, Mn2+, Fe2+, Fe3+, Co2+, Ni2+ and Cu2+) were substituted for sodium ions in phosphates added as nucleating agents in the melt system, and their upper limiting temperatures were measured by thermal cycling. Deactivation was observed with 7 of these cation-substituted phosphates. The limiting temperatures of the substituted phosphates all differed within the range of 12 to 22 K above the melting point. The degree of similarity in the lattice shapes of unit cell planes between the crystals of sodium acetate trihydrate and the phosphates was quantified, but no reasonable correlation was found between the similarity and the limiting temperature. On the other hand, a clear correlation between the limiting temperature and the solubility of the phosphate in water was reconfirmed. The experimental findings suggested that the bonding force between solid surfaces of sodium acetate trihydrate crystals and the precipitated phosphate, which is mediated by the hydrating water molecules, is a physical factor controlling the limiting temperature.

• 出版日期2017